The present invention relates to a reflective liquid crystal display structure in which peripheral driver circuits are integrated with other circuitry.
A structure comprising a substrate on which an active matrix circuit and peripheral driver circuits for driving the active matrix circuit are all packed is known. At least one TFT is disposed at each pixel of the active matrix circuit. This structure is known as the active matrix display integrated with peripheral driver circuits.
Generally, a peripheral driver circuit is composed of circuits (typified by shift registers) and buffer circuits for supplying signals to the active matrix circuit. However, it is considered that the trend is toward constructing circuits handling image information and various timing signals from TFTs and toward integrating these TFTs as peripheral driver circuits with the active matrix circuit on the same substrate. In the past, such circuits have been composed of externally attached ICs.
Essentially, the active matrix circuit comprises source lines and gate lines arranged in rows and columns. TFTs are disposed near the intersections. On the other hand, the peripheral driver circuit is based on a CMOS circuit. However, it is expected that the circuit will become more complex in configuration. In this structure, the use of multilevel wiring is required to reduce the area occupied. However, if an additional layer is formed to achieve the multilevel wiring, the fabrication process is complicated.
It is an object of the present invention to provide a reflective liquid crystal display panel on which an active matrix circuit is integrated with peripheral driver circuits having multilevel wiring that can be accomplished with greater ease than conventional.
The invention disclosed herein is directed to a reflective liquid crystal display. This kind of liquid crystal display uses metal electrodes as reflective electrodes. For example, the metal electrodes consist chiefly of aluminum.
The present invention has been made by taking notice of the material of the reflective electrodes. Conducting lines arranged in the peripheral driver circuits are formed out of the same material as the pixel electrodes simultaneously with the formation of-the pixel electrodes.
In this way, multilevel wiring necessary for the peripheral driver circuits can be constructed without any additional process step, though the pattern is made more complex.
Since the reflective electrodes can be made of a low-resistivity material such as aluminum, they are preferably used to form conducting lines in the peripheral driver circuits.
In the transmissive liquid crystal display, pixel electrodes are made of a material having a relatively high resistivity such as ITO. Therefore, the present invention is not adapted to be used in the transmissive liquid crystal display.
The peripheral, driver circuits referred to herein include shift register circuits and buffer circuits that directly drive the active matrix circuits. Furthermore, circuits for producing various timing signals, circuits for handling image information, various memory devices, and arithmetic units are included.
The present invention provides a reflective liquid crystal display panel comprising an active matrix circuit formed on a substrate, peripheral driver circuits including circuits for driving the active matrix circuit, and reflective pixel electrodes arranged in rows and columns in the active matrix circuit. The active matrix circuit and the peripheral driver circuits are formed on the same substrate. The active matrix circuit is composed of TFTs. The peripheral driver circuits are also composed of TFTs. The peripheral driver circuits have conducting lines made of the same material as the reflective pixel electrodes.
In the active matrix circuit of the liquid crystal display of the structure described above, source lines and the gate lines are arranged in rows and columns. TFTs are disposed near the intersections of these source and gate lines. The drains of the TFTs are disposed at the pixel electrodes.
Peripheral circuits include circuits composed of shift register circuits, analog switches, buffers, and so on. This kind of circuit is ordinarily referred to as a peripheral driver circuit. Further peripheral circuits include oscillator circuits, circuits handling image information, and circuits equipped with memory devices or the like.
It is considered that future trend will be toward adding various other functions to the above-described peripheral circuits. Accordingly, the peripheral circuits referred to herein embrace circuitry having various functions (known as a system-on-panel), as well as circuits for driving an active matrix circuit.
TFTs can take various forms such as top-gate type, bottom-gate type, and multigate type in which numerous TFTs are equivalently connected in series.
Preferably, the material of the reflective electrodes has a high reflectivity and a low resistivity, as typified by silver, aluminum, and silver-aluminum alloys.
For example, in the case of the VGA standard (640xc3x97480 pixels), the frame of image is rewritten or refreshed at a rate of 60 times per second. This requires that the horizontal scanning driver circuit (peripheral driver circuit on the side of source lines) operate at a rate of 640xc3x97480xc3x9760=18.5 MHz. In the case of the XGA standard (1024xc3x97768 pixels), an operating speed. of 1024xc3x97768xc3x9760=47 MHz is necessitated.
In these cases, the resistivity of the conducting lines in the peripheral driver circuits should be made as low as possible. The present invention is quite useful for this purpose.
A specific example in which the conducting lines in peripheral circuits are made of the same material as the reflective pixel electrodes is shown in FIG. 6. When the pixel electrodes, 141, are formed, the conducting lines, 142, in the peripheral circuits are formed from the same material as the pixel electrodes.
This is achieved by forming the pattern of the pixel electrodes 141 and the pattern of the conducting lines 142 simultaneously out of conducting film (not shown) that forms the pixel electrodes. This can be checked by taking an electron microscope image of a cross section of the structure, determining whether the pixel electrodes and the conducting lines are present in the common layer, determining whether they are equal in film thickness, and measuring the doping level to know whether the material is uniform or not.
Other objects and features of the invention will appear in the course of the description thereof, which follows.